Transmitting electronic mail (e-mail) messages is one of the major functions served by the Internet. With its phenomenal growth in the late 1990s, the Internet has replaced several proprietary e-mail messaging systems and become the ubiquitous global network for e-mail messaging.
Due to the cost and technical complexity involved in hosting an e-mail server on the Internet, many small business entities and individual users do not host their own Internet e-mail servers. Instead, they use Internet mail servers provided by their Internet Service Providers (ISPs) to transmit and receive e-mail messages to and from the Internet. In such an arrangement, Internet e-mail messages destined for users on the local area network (LAN) of a business entity are first routed through the Internet to the ISP's Internet mail server and held in a mailbox for that business entity. A mail server of the local area network then uses a mail connector software module to connect to the Internet mail server of the ISP and download the e-mail messages from the mailbox at the Internet mail server, and distributes the downloaded messages to their intended recipients.
Currently, most mail servers implement the Post Office Protocol Version 3 (POP3) for handling the exchange of e-mail messages, and the mail connector used for downloading e-mail messages from the Internet mail server is programmed to operate according to the POP3 requirements. Other e-mail access protocols have been proposed, however, with the intent to provide enhanced e-mail messaging functionality. One example is the Web Distributed Authoring and Versioning (Web DAV) protocol. Those e-mail access protocols not only define different e-mail access operations but also use different message formats. For instance, the POP3 requires e-mail messages to be in the Internet Message Format (IMF) defined in RFC 822 of the Internet Engineering Task Force (IETF), while the Web DAV protocol requires the e-mail messages to be in the Extensible Markup Language (XML) format.
Due to the importance of Internet e-mail messaging, more e-mail access protocols and message formats will likely be proposed and implemented in the future. It is expected that a local area network may have e-mail accounts with multiple Internet mail servers that support different e-mail access protocols. Thus, the mail connector software has to have the ability to access e-mail messages at the Internet mail servers according to the different protocols and the ability to handle different message formats. From the viewpoint of a software developer, however, it is desirable to minimize the amount of reprogramming work that has to done to modify the mail connector software or the like to provide support for new e-mail access protocols and message formats. Accordingly, there is a need for a software module for use by a local mail server to access e-mail messages at Internet mail servers that can be easily extended to support various e-mail access protocols and message formats.